1. Two Sum

Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

一样遍历，遍历过的数据键值交换存入字典中，遍历新值的时候计算结果直接在字典中寻找。

class Solution(object):
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        dic = {}
        
        for i in range(len(nums)):
            item = nums[i]
            if (target - item) in dic:
                return [dic[target - item], i]
            dic[item] = i